Petrocephalus leo sp. nov. is a small-sized species within the genus (maximum SL observed = 78.9 mm; holotype = 76.1 mm). Body ovoid, 2.9–3.4 times longer than high (paratype average = 3.2, holotype = 3.3) and laterally compressed. Head length between 3.1 and 3.7 times in standard length (paratype average = 3.5, holotype = 3.6). Snout short (5.2 ≤ HL/SNL ≤ 7.4, paratype average = 5.9, holotype = 6.0) and round. Mouth small (3.8 ≤ HL/MW ≤ 4.9, paratype average = 4.2, holotype = 3.8), sub-terminal, opening under posterior half of eye. Teeth small and bicuspid, 7–9 in a single row in the upper jaw (paratype median = 8, holotype = 8), 15–23 in a single row in lower jaw (paratype median = 18, holotype = 18). Dorsal and anal fins originate in posterior half of body (1.5 ≤ SL/PDD ≤ 1.6 and 1.6 ≤ SL/PAD ≤ 1.7, respectively). Pre-dorsal distance slightly greater than pre-anal distance (1.0 ≤ PDD/ PAD ≤ 1.1). Dorsal fin with 21–24 branched rays (paratype median = 22, holotype = 22). Anal fin with 26–29 branched rays (paratype median = 27, holotype = 27). Body scaled except for head. Lateral line visible and complete with 34–38 (paratype median = 36, holotype = 37) pored scales along its length. Twelve scales around caudal peduncle. Nine to 12 scales (paratype average = 10, holotype = 9) between anterior base of anal fin and lateral line. Caudal peduncle thin (1.9 ≤ CPL/CPD ≤ 2.5, paratype average = 2.2, holotype = 2.2). Twelve scales around caudal peduncle. Skin on head thick, turning opaque with formalin fixation. Knollenorgans visible, but not clustered into the three distinct rosettes as described in Harder (1968).
